In recent years, with the increasing cost of energy, the regulations on energy consumption have been increasingly stringent in every country. Taking energy conservation in the manufacture industry for example, motors are accounted for more than 70 percentages of the overall electricity consumption. Therefore, how to increase the energy efficiency of the motors has become an important issue. Among different motors, the brushless permanent magnet motor offers a simple design that is easy to maintain and has high efficiency. In particular, an axial flux motor (AFM) of the brushless permanent magnet motor is the one having a smaller length-diameter ratio and suitable for thinner design.
Magnet is one of key components of the brushless permanent magnet motor that determines the performance and speed thereof. Therefore, methods, that can improve magnets in increasing the energy product, better control of the lines of flux inside the motor and suppressing the flux leakage, can increase the energy efficiency of motors. Hence, the capability of the magnets is a crucial issue in the development of the motors.
Among various types of magnets, rare-earth (material) magnets generally are strong permanent magnets made from alloys of rare earth elements. Motors using rare-earth magnet have higher energy product and better torque density, thus to be widely used in the mechanical and electrical applications.
However, the cost of rare earth metals has surged almost threefold in recent years. Hence, price of the motors that use rare-earth magnet has risen. Rising price forces the industry to endeavor to design a motor that utilizes less rare-earth magnets and levels up the energy efficiency of the motors.